DESCRIPTION (APPLICANT'S ABSTRACT): The care of persons with Alzheimer's disease and related dementias (AD) is a prevalent, costly, and growing issue, particularly for long-term care settings, where nearly 1.5 million persons with AD reside. Among the most troublesome management issues in AD are a tried of interrelated problems-sleep/wake disorders, depressive symptoms, and agitation. Current management of these conditions relies extensively on psychoactive medications, which have limited effectiveness and significant adverse effects. Demonstration of an effective, low-risk alternative treatment could have a favorable impact on long-term care nationwide. One promising alternative, high intensity light, has been demonstrated to produce biochemical and physiological effects on the systems that mediate these behaviors, and to have produced significant improvement in pilot and preliminary studies. The proposed project is a clinical trial with crossover, of the effect of high intensity, low glare, ambient daytime light on sleep/wake patterns, depressive symptoms, and agitation in nursing home residents with AD. It will be conducted in a licensed skilled nursing facility within a state psychiatric hospital, which manages 45 residents with AD. It will employ a 4 treatment, 12 period crossover design, with the treatments consisting of a) morning high intensity light, b) evening high intensity light, c) full day high intensity light, and d) the control (preexisting) lighting. The intervention (applied separately to each of 3 wards) will consist of fixtures that produce even, non-glare light averaging 2500-3000 lux in all public areas of the facility. Sleep/activity will be measured using wrist motion sensors; depressive symptoms will be measured using the Cornell Depression Index and the Philadelphia Geriatric Center Affect Rating Scale; and agitation will be measured using computer-assisted direct observations and the Cohen-Mansfield Agitation Inventory. Light exposure will be documented using wrist photocells. Secondary outcomes will include staff depression and reported hassles. Data collection will continue for one year to allow analyses to adjust for seasonal differences in outdoor light levels.